Heavy fighting was reported in the Wardhiigley district in northeast Mogadishu, according to African Union officials. Mortars and gunfire could be heard near the African Union base on Monday.

Troops killed two apparent suicide bombers dressed in Somali uniforms before they were able to detonate bombs strapped to their bodies, African Union officials said. During a gunfight, two African Union soldiers were killed.

"In the midst of a famine seizing Somalia, the extremists are choosing to focus on killing, not saving life," said Lt. Col. Paddy Ankunda, the spokesman for African Union forces. "The extremists are using desperate measures to achieve their ends through their willingness to use brutal violence during the holy month of Ramadan."

Al-Shabaab has launched Ramadan offensives against Somali and African Union forces every year since the organization sent troops to Mogadishu in 2007, according to the African Union. Ramadan began Monday.

The African Union said Al-Shabaab appeared to be massing fighters in the city and preparing for additional attacks.

Last week, African Union forces mounted an offensive against Al-Shabaab aimed at giving humanitarian organizations more breathing room to deliver food and supplies as the country tries to deal with a crippling drought and famine.

On June 20, the United Nations declared a famine in two regions of southern Somalia for the first time since 1991, according to the organization.

The rate of malnutrition in Somalia's rebel-held south is the highest in the world, approaching half the population, the U.N. said.

U.N. officials are concerned the fighting could interfere with their ability to deliver humanitarian aid in Mogadishu, but it has not, Valerie Amos, under-secretary-general for humanitarian affairs, said Monday.

The U.N. needs to raise $2.4 billion to help prevent the famine from spreading, Amos said. Donors have contributed $1 billion, she said.